Passenger doesn't seem to be running (Capistrano/Rails/Apache/Ubuntu)
I needed to customize the instance registry directory, as suggested by Tony Vincent:
/etc/apache2/mods-enabled/passenger.conf on the server:
PassengerInstanceRegistryDir /home/MYUSER/passenger_tempconfig/deploy/production.rb in the Rails app:
set :default_env, { 'PASSENGER_INSTANCE_REGISTRY_DIR' => '/home/MYUSER/passenger_temp' }
Sorry to harp on this but did you run passenger-config validate-install on the ubuntu server (not osx)? Same for passenger-memory-stats and sudo apache2ctl restart.
Based on /tmp not having a passenger.randomstring dir, it sounds like you are confusing local and remote commands. /tmp is the default location for PassengerInstanceRegistryDirs on Ubuntu so if Passenger is running there should be a dir in /tmp that starts with passenger..